I yellowcake bombed a swarm of scarab beatles today, and noticed that it did not drop a palm frond. When I encountered another swarm, I looked at the list of items and the frond was not marked as "cond". From the wiki page I linked, it is noted there (FWIW) that it is a conditional drop; I can confirm that the yellowcake bomb did not force it to drop.
I did not try yet on the other monsters that drop the palm frond (blur, oasis monster, rolling stone) and the wiki does not mention it on their pages -- likely because the swarm is the one of those usually targetted with YRs for the mojo filter. I would expect that TPTB have the item itself being conditional on all the monsters, but won't be able to confirm that until I get a chance to YR the others and fail to get a frond drop.
I did not try yet on the other monsters that drop the palm frond (blur, oasis monster, rolling stone) and the wiki does not mention it on their pages -- likely because the swarm is the one of those usually targetted with YRs for the mojo filter. I would expect that TPTB have the item itself being conditional on all the monsters, but won't be able to confirm that until I get a chance to YR the others and fail to get a frond drop.